1. Field of the Invention
This invention relates to a bending furnace for glazings comprising several heating cells, a station for bending by pressing and at least one cooling station, a system of transport of glazings each laid on a bending ring mounted on a mobile carriage, the carriages being coupled to one another and transported through the bending furnace intermittently by a machine installed at the end of the bending furnace pulling the carriage train, and means to stop and position the carriages precisely in the station for bending by pressing.
2. Description of the Related Art
Bending furnaces comprise the main part of installations for production of glass sheets bent in pairs for an assembly in a composite laminated glazing. When the bending temperature is reached, the glass sheets are deformed under the effect of their own weight and sink on the bending ring, whose shape the periphery of the sheet thus assumes.
To complete this bending by sinking on the bending ring, a pressing can be provided by a solid upper form mounted in one of the last heating cells, above the plane of transport of the glazings, which upper form is lowered so as to press the glass sheet against the lower ring (U.S. Pat. No. 4 778 507). This pressing makes it possible to obtain complex shapes, optionally to lower the bending temperature and to increase the precision and the reproducibility of the shapes obtained.
The bending ring, at the moment of the pressing operation, should occupy a given position which is precisely perpendicular to the upper bending form. For this purpose, it is known to provide means to stop the carriages in a reference position. Further, the upper bending form and the carriage carrying the peripheral ring are equipped with a mechanical locking device, of the type with pins coming to engage in a conical housing.
In a bending furnace of this type, the intermittent transport of the carriage train is performed by use of a pulling machine installed at the output of the furnace and which has a driving element engaged at each step on a new carriage. This element being installed outside the furnace, the directly engaged carriage is always separated from the carriage located in the pressing station by an entire series of other carriages. This great distance between the site where the precise positioning is necessary and that for control of the movements of the carriages makes accurate positioning very difficult, especially as all the parts undergo significant deformations following thermal expansion. The temperature is actually 500.degree. C. and more in the station for bending by pressing, but this temperature varies enormously from one end of the furnace to the other and the carriage train which is between the pressing station and the output of the pulling machine is subject to notable variations of length which in total can reach about 20 cm.